Ionizing Radiation and Tumor Production

Ionizing radiation has long been a promising agent for studying the mechanism of cancer induction. The dose of radiation delivered to a given tissue can usually be determined with much greater precision than can the dose of a chemical agent. By varying the radiation dose, or dose rate, while holding other factors constant, and then measuring the yield of malignant conditions, the investigator can hope to quantitate the kinetics of the cancer induction process. To be sure, there are many obstacles. For example, to assay for malignancy after exposure of somatic cells to radiation is much more difficult than to assay for chromosomal or gene damage after exposure of germ cells to radiation. Doses as low as several hundred rads, when delivered to the organism acutely, may not only kill large numbers of somatic cells but may disrupt the immunological and hormonal systems in such a way as to modify the yield of malignancies in a complex manner.